Investments in fixed maturity securities - Amortized cost and estimated fair value of securities with fixed maturities (Detail) - USD ($) $ in Millions	Sep. 30, 2022	Dec. 31, 2021
Summary of Investment Holdings [Line Items]
Due in one year or less - amortized cost	$ 7,904
Due after one year through five years - amortized cost	10,201
Due after five years through ten years - amortized cost	460
Due after ten years - amortized cost	82
Amortized cost of fixed maturity securities	18,845	$ 15,964
Due in one year or less - fair value	7,753
Due after one year through five years - fair value	9,895
Due after five years through ten years - fair value	654
Due after ten years - fair value	85
Fair value of fixed maturity securities	18,602	$ 16,434
Mortgage-backed securities [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of mortgage-backed securities	198
Fair value of mortgage-backed securities	$ 215

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27161-111563

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=124258926&loc=SL82898722-210454

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+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 3
-URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27198-111563

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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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